Convert from pound [troy] to arroba [Spain]

Unit Definition (pound [troy])
The pound [troy] is a second traditional unit of mass or weight. The troy pound, named for the French market town of Troyes, was the unit used in England by apothecaries and jewelers. The troy pound is divided into 12 ounces like the Roman pound. One troy pound is 373.242 grams, or exactly 144/175 = 0.822 858 avoirdupois pounds (13.165 72 avoirdupois ounces). The troy and avoirdupois pounds are connected by the grain: there are 5760 grains in a troy pound and 7000 grains in an avoirdupois pound.

Unit Definition (arroba [Spain])
The arroba [Spain] is a traditional unit of weight in Spain and Portugal, equal to 1/4 quintal. However, the Spanish and Portuguese quintals are of different sizes. In Spain, the arroba equals 25.36 pounds (11.50 kilograms); arrobas of very similar sizes were established in the Spanish speaking countries of Latin America. The arroba has also been used as a metric unit equal to exactly 15 kilograms. The name of the unit comes from ar rub', Arabic for "the quarter."